The present invention relates to an electrophotographic-type image forming apparatus.
The electrophotographic-type image forming apparatus is composed of an output engine for charging a photoconductor, selectively exposing the charged photoconductor to form an electrostatic latent image while scanning the charged photoconductor, and feeding a developer to the electrostatic latent image so as to develop it, and a controller for converting image data received from an external or other component to printing data consisting of data sets continuing in a main scanning direction of the output engine and inputting the image data into the output engine for image output.
The output engine applies a laser beam to the photoconductor to lower its potential, so that toner is adsorbed and hence a toner image is developed. Accordingly, nominal resolution of the output engine is determined by the diameter of a laser beam which exposes the photoconductor. However, while the resolution in a sub scanning direction depends on the diameter of the laser beam which exposes the photoconductor, the resolution in the main scanning direction depends on a travel distance of a laser beam, corresponding to a time during which an applied amount of the laser beam, sufficient enough to lower the potential of the photoconductor to the level of the toner adsorption, can be secured when the focus of the laser beam moves at a specified speed on the photoconductor.
Thus, the controller of a conventional image forming apparatus converts the image data to printing data having the nominal resolution of the output engine with respect to the sub scanning direction and having upper limit resolution with respect to the main scanning direction.
More specifically, the output engine attempts to apply a laser beam in compliance with high-definition data in the main scanning direction to be inputted and to develop dots with definition higher than the nominal resolution. However, independent dots of high definition cannot secure an enough application amount even when the laser beam is applied, which causes insufficient attachment of the toner, resulting in substantial failure of development.
In the field of image forming apparatuses, a technology is publicly known, in which the number of dots to be outputted based on the printing data is counted by a dot counter to estimate the consumption of toner. When a conventional image forming apparatus outputs, in the main scanning direction, an image containing a number of small independent dots which cannot be developed by their output engines, the toner consumption estimated based on an integrated value from the dot counter sometimes becomes larger than actual toner consumption, and thereby issues a toner empty alert regardless of the presence of enough remaining toner.
Disclosed in JP 2001-147563 A and US 2005/0025509 A1 is a technology in which a patch image is formed so as to check the concentration of developed toner by a sensor so that laser beam outputs are adjusted and corrected in order to correct changes in image concentration attributed to changes in laser output caused by contamination.
Disclosed in JP 2005-43617 A is a technology in which a patch pattern is outputted so as to check the concentration of developed toner by a sensor and to correct printing data in order to achieve appropriate tone reproduction.
Although these technologies increase the accuracy in estimation of toner consumption in halftone, they cannot eliminate estimation error in toner consumption caused by inability to develop the aforementioned fine dots.